1. Field of the Invention
The present invention relates generally to injection molding, and more particularly, to the configuration of an injection molding machine for forming objects from a moldable material.
2. Description of the Related Art
There are known prior art injection molding machines which inject moldable material into a tool comprised of upper and lower mold cavity halves. In some instances where permitted by the shape of the mold cavity, the upper and lower mold cavity halves are pivotably connected together at one end. The tool is movable on a work table by an operator to be placed below a vertically movable upper platen. The upper platen is moved downwardly onto the upper mold cavity half to press the upper and lower mold cavity halves together in preparation for injection of moldable material into the mold cavity. After injection of the moldable material into the mold cavity the upper platen is raised vertically to relieve the locking force on the tool. The operator then withdraws the tool from below the upper platen and pivotally opens the upper mold cavity half to retract the molded object from the cavity. Such prior art machines typically utilize an hydraulic drive mechanism for vertically moving the upper platen and for applying the locking force to the upper mold cavity half.
Other prior art injection molding machines, such as described in U.S. Pat. No. 3,523,328, include apparatus for initially vertically lifting an upper mold cavity half a predetermined distance to expose the object formed in the mold cavity, and then, in a subsequent portion of the opening cycle, the upper mold cavity half is tilted arcuately to expose the lower mold cavity half and the molded object for inspection and cleaning.
Each of the prior art injection molding machines described above have significant drawbacks. The machines which utilize a vertically moving upper platen to press the upper and lower mold cavity halves together must apply a very high force to the abutting mold cavity halves in order to hold the mold cavity halves together and resist the forces generated from high pressure injection of moldable material into the mold cavity. Such high forces may cause damage to the tool mold where foreign objects are present between the abutting surfaces of the upper and lower mold cavity halves. For intricate configurations requiring high tolerances, such as where the molded object is to be used as a pattern for turbine engine components, the cost of the tool may exceed $100,000 and, once damaged, must be replaced or repaired.
Furthermore, since an operator must physically move the tool away from the space immediately below the upper platen to have sufficient space to pivotally open the upper and lower mold cavity halves, there is a decrease in efficiency of the molding process due to the extent of operator involvement. Also, such extensive operator manipulations increases the chances of injury to the operator from exposure to the moving upper platen. Furthermore, studies have shown that long term exposure to the operator manipulations required to open and close the tool result in a significant loss of dexterity in the hands.
With machines of the type disclosed in U.S. Pat. No. 3,523,328, where the upper mold cavity is moved vertically away from the lower mold cavity just prior to removing the molded object, there is a chance of damaging the surface of the molded object particularly where those surfaces ar rounded and designed to high tolerances such as is the case for turbine engine components.
Therefore, it is an object of the present invention to provide an apparatus for forming objects from a moldable material wherein the locking force holding the upper and lower halves of the mold cavity closed during injection of moldable material into the mold cavity is significantly less than a separation force which the apparatus is capable of resisting and which tends to urge the upper and lower mold cavity halves apart. In this manner, damage to the mold caused by pressing the upper and lower cavity halves together with a high force when foreign objects are present is significantly reduced.
It is a further object of the present invention to provide an apparatus for forming objects from a moldable material which eliminates the need for an upper platen in a conventional sense thereby increasing the overall efficiency and safety of the molding process.
It is still a further object of the present invention to provide an injection molding machine which automatically opens a mold cavity by pivotally moving the upper mold cavity half in an arcuate path away from the lower mold cavity half to thereby reduce operator involvement and decrease the chances of damaging the surface of the molded object.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.